vice president biden attended a phepl i can't tell at the crash site of flight 93 in shanksville, pennsylvania, where 40 passengers sacrificed themselves to defeat the hijackers. later in this broadcast, chip reid will have the story of one of the victims and a discovery on her computer, a dream that is now being fulfilled. now, imagine this: the next president is about to take office when he suddenly disappears. well, it has just happened in china. everyone wants to know what has happened to xi jinping, the man who is supposed to take over next month. our state department correspondent margaret brennan has been looking into this. >> reporter: the last photo of the man expected to be china's next president, 59-year-old xi jinping, was taken on september 1. for the past ten days, he has not shown up at any scheduled public events. his apparent disappearance has sparked speculation in the world press. when asked about it at a news conference, a chinese foreign ministry spokesman refused to comment. "i hope that you can ask more serious questions" he said. adding to the mystery: government sensor